If a runner is detached from a skier's boot on a slope, there is danger that it may slide downhill and get lost or perhaps hurt other persons. The use of safety straps, designed to limit the extent to which the runner can separate from the boot, eliminates this risk but may have serious consequences for the skier himself as the runner is constrained in the case of a spill to follow the fallen skier, thus possibly injuring him.
It has therefore already been proposed to equip each ski runner with a self-activating brake designed to bite into the snow upon its release from the boot, the brake including a mobile element which is pivoted to the runner and in use is retracted above the lower surface of the latter but projects downwardly beyond that surface as soon as the boot is detached. Conventional devices of this nature, however, are only limitedly effective, depending on such factors as the quality of the snow, the steepness of the slope and the relative orientation of the runner and the slope at the instant of detachment. Thus, a ski brake designed to prevent forward sliding may be totally ineffective in the backward direction.